Solid catalysts containing metals, metal oxides or sulfides, play a key role in the refining of petroleum to clean fuels. After use, the spent catalysts are discarded as solid waste. In refineries, the spent catalysts discarded from hydroprocessing units form a major part of these solid wastes. Disposal of spent hydroprocessing catalysts requires fulfillment with environmental regulations because of their hazardous nature and toxic chemicals content and they may present significant environmental problems, as landfill disposal is no longer accepted. Several alternative methods such as disposal in landfills, reclamation of metals, regeneration/rejuvenation and reuse, and utilization as raw materials to produce other useful products are available to the refiners to deal with the spent catalyst problem. The various options available for handling the spent catalyst problem have been reviewed by Marafi and Stanislaus in some recent papers (Journal of Hazardous Materials B, 101 (2003) 123-132; Resources, Conservation and Recycling 52 (2008) 859-873; Resources, Conservation and Recycling 53 (2008) 1-26).
As pointed out in the aforementioned papers, utilization of spent hydroprocessing catalysts in the production of valuable products is an attractive option from environmental and economical points of view. For example, spent fluid catalytic cracking catalysts have been successfully used in cement production. The spent hydroprocessing catalysts containing Mo, Co or Ni and vanadium have been used for recovering valuable metals and alumina. Several methods such as chlorination, acid leaching, alkali leaching, bioleaching, roasting with soda salts, etc., have been studied and reported in open literature and patents have issued for the recovery of Mo, Ni, V and Co from the spent catalysts. Several companies have also been established for large scale reclamation of metals and metal compounds from spent hydroprocessing catalysts. Alumina is the main component of hydroprocessing catalysts, accounting for more than 70 wt. % of the fresh catalysts.
The present invention provide-s a method of boehmite synthesis from spent hydroprocessing catalyst. The recovery of pure boehmite deserves attention because of its wide applications i.e., for reuse as catalyst support, for preparation of catalysts, sorbents, etc. The use of similar supports and catalysts and routes for metals recovery and alumina reported in the literature are described in the following patents.
U.S. Pat. No. 4,495,157 proposed oxygen pressure leaching of spent hydrodesulfurization catalyst for metal recovery using sodium carbonate in the leach slurry. The process and other proposals are operative but are still subject to improvement by way of reducing cost, improving metal recovery, improving filterability and reducing weight and volume of solids generated in the leaching steps and affording lower temperatures and pressures for leaching.
US Pat. Publication No. 2008/0025891, describes a process for recovering alumina values from a first liquor stream containing aluminate ions and hydroxyl ions in solution by forming an aluminium bearing layered double hydroxide. This process further relates to the use of aluminium-bearing layered double hydroxides (LDHs) to improve recovery of alumina values from bauxite using a modified form of the Bayer process. However, the recovery of alumina as boehmite from spent catalyst materials is not reported in this patent.
U.S. Pat. No. 4,657,745, reports a process for the recovery of aluminum, molybdenum and at least one other metal selected from the group consisting of nickel and cobalt from a spent catalyst. The spent catalyst (CoMo/Al2O3 was treated with H2SO4 in the presence of H2S under pressure (7.5-15 atm) in an autoclave at 100-200° C. The presence of H2S during leaching with H2SO4 results in the precipitation of Mo and Co as sulfides while the Al2O3 is converted to soluble (Al2SO4)3. The metal sulfides were separated from the Al2(SO4)3 solution and subjected to oxidation under pressure in an autoclave to convert MoS2 to solid molybdic acid and the CoS to CoSO4. The molybdic acid was separated by filtration from the CoSO4 solution. The cobalt was recovered by ion exchange.
U.S. Pat. No. 4,142,871 discloses a process for utilizing spent catalysts in a process which combines the formation of alumina abrasives with the recovery of nickel or cobalt materials from the catalysts. The Zeiringer process melts the catalyst material containing the heavy metal, cools the material and mechanically separates the alumina-containing melt component from the metal alloy residue.
U.S. Pat. No. 4,029,495 also disclose a process for separating heavy metal materials such as nickel and cobalt from spent catalyst support materials. In the process, the spent catalyst material is heated to a sintering temperature to cause aggregation of the metal component. The mixture then may be either crushed and separated or further heated to from 1480° to 1580° C. to separate the molten heavy metal phase and a second melted phase comprising the carrier. The carrier may be separated by pouring off the top layer for use in formation of ceramic fibers and pouring the bottom layer into a mold to form ingots.
U.S. Pat. No. 5,702,500, deals with the treatment of materials containing alumina, silica, nickel, cobalt, molybdenum and vanadium. More specifically, the Patent discloses a treatment of spent catalysts and the recovery of valuable metals such as molybdenum, vanadium, nickel, cobalt and fused alumina by a combination of hydrometallurgical and pyrometallurgical processes.
U.S. Pat. No. 4,087,510, discloses mixing one part of finely ground spent catalysts with 0.5 to 0.9 parts of sodium carbonate and roasting the mixture at 650°-850° C. for about 1 to 2 hours. The roasted material is then dissolved in water to recover most of the molybdenum and vanadium in solution, along with 1-2% of the alumina contained in the catalyst. This process, however, does not recover aluminum, nickel or cobalt in commercially acceptable forms.
US Pat. Publication No. 2006/0258531 discloses a process for manufacturing a hydrorefining catalyst that exhibits high activity in a specific reaction by using a large pore diameter (50 to 2000 nm) catalyst that has been used in hydrorefining. The metal recovery mainly vanadium and nickel metals are from these spent hydrodemetallization catalyst that were carried out on regenerated catalyst and thus, established a method for metal recovered from the used regenerated catalyst. In this process metals components are recovered more efficiently, and the spent catalyst can be reused to manufacture as a regenerated catalyst that exhibits high reaction activity.
U.S. Pat. No. 4,349,381 discloses a process for smelting spent catalysts using two furnaces. Slag, produced from melting spent catalysts in the first furnace, is transported to a second furnace for adjustment of composition and quantity. This process however, does not address the recovery of molybdenum and vanadium as separate saleable products.
U.S. Pat. No. 3,567,433, discloses a process where ammonium carbonate solution used to extract metals by leaching of metals from hydrotreating spent catalysts and recovered more than 90% of Mo and V, and 60-70% of Ni by using leaching time and temperature, 1 h and 150° C., respectively
U.S. Pat. No. 4,514,368, deals with an invention that relates to leaching of nickel, cobalt, molybdenum, tungsten, and vanadium from spent hydroprocessing catalysts, where inventor was able to extract at least 85% of Mo, 75-85% of V, 75-80 Ni and 45% of Co from decoked spent catalysts by leaching with an aqueous solution of ammonia containing an ammonium salt such as ammonium carbonate or ammonium sulfate. The pH of the ammonia solution was in the range 9.5-11 and extraction temperature was in range 85-95° C. Decoking temperature and leaching time were found to have a significant effect on the extracting of Ni and Co. Nickel extraction suffered as the roasting temperature during the decoking process was increased above 600° C. Inventor also found leaching time had a strong influence on Co recovery.
Most of the aforesaid patents are used to recover metals (Ni, V. Co, and Mo) while none of them clearly indicated alumina recovery as boehmite from spent hydroprocessing catalyst, which make the present invention different than those of the prior art patents. The present invention is an investigation of a spent catalyst where alumina support recovery is obtained at high purity and the nature of recovered solid has better textural properties, which is attributed to the method of alumina recovery. The present invention also provides a procedure in order to obtain boehmite from spent hydroprocessing catalysts and its textural property modification.
The present invention aims to overcome the problems and disadvantages of the prior art by providing a simple, and efficient procedure for complete extraction and recovery of valuable components of the spent hydroprocessing catalysts including alumina that could be reused in catalyst preparation. Surprisingly, little effort has been made in the prior art in seeking to recover the alumina support, which accounts for about sixty percent of the weight of spent catalysts, in the form of boehmite [AlO(OH)] with desirable textural properties for reuse as support material in the preparation of new catalysts as well as in many other applications.